Method and arrangement for blood pressure measurement

ABSTRACT

A method and arrangement for blood pressure measurement are disclosed. In the method, a variable, compressive, acting pressure is applied to a compression, such as a person&#39;s extremity, by a pressure generator, and simultaneously, the effect of the variable acting pressure on the extremity is measured at a second point, the second point being farther from the heart than the compression point. The method determines diastolic and systolic pressure. The measured value of the variable acting pressure acting on the compression point is transferred to an interpreting unit, which also receives a pressure pulse generated by the heart. The pressure pulse is measured by a sensor at the second point for determining the effect of the variable acting pressure on the extremity. Further, diastolic pressure is determined int he interpreting unit based on the variable acting pressure, as the pressure when the interpreting unit detects a change in a trend of a characteristic of the pressure pulse indicative of magnitude.

FIELD OF THE INVENTION

The invention relates to a method for blood pressure measurement, inwhich method a variable compressive acting pressure is applied to ameasuring point, such as a person's extremity or the like, at acompression point by a pressure generator, and at the same time theeffect of the variable acting pressure on the artery is measured at asecond point, the second point being located farther away from theheart, i.e. closer to the end point of peripheral circulation, than thecompression point to which the acting pressure is applied, and in whichmethod diastolic pressure is determined.

The invention also relates to a method for blood pressure measurement,in which method a variable compressive acting pressure is applied to ameasuring point, such as a person's extremity or the like, at acompression point by a pressure generator, and at the same time theeffect of the variable acting pressure on the artery is measured at asecond point, the second point being located farther away from theheart, i.e. closer to the end point of peripheral circulation, than thecompression point to which the acting pressure is applied, and in whichmethod systolic pressure is determined.

The invention further relates to an arrangement for blood pressuremeasurement, comprising a pressure generator for applying a compressiveacting pressure to a measuring point, such as a person's extremity orthe like, the arrangement comprising an acting pressure measuringelement, the arrangement further comprising an interpreting unitarranged to determine diastolic pressure, the arrangement comprising asensor for simultaneous measurement of the effect of the variable actingpressure on an artery at a second point, said second point being fartheraway from the heart, i.e. closer to the end point of peripheralcirculation, than the compression point to which the acting pressure isapplied.

The invention also relates to an arrangement for blood pressuremeasurement, comprising a pressure generator for applying a compressiveacting pressure to a measuring point, such as a person's extremity orthe like, the arrangement comprising an acting pressure measuringelement, the arrangement further comprising an interpreting unitarranged to determine systolic pressure, the arrangement comprising asensor for simultaneous measurement of the effect of the variable actingpressure on an artery at a second point, said second point being fartheraway from the heart, i.e. closer to the end point of peripheralcirculation, than the compression point to which the acting pressure isapplied.

BACKGROUND OF THE INVENTION

The heart pumps and causes blood to flow in the blood vessels, arteriesand veins. The pumping produces pressure in the blood, i.e. bloodpressure. Blood pressure is particularly affected by heartbeat and theresistance provided by peripheral circulation. Psychic factors,medication, smoking and other factors, such as a person's state, i.e.whether a person is asleep or awake, are also important.

The terms systolic pressure, diastolic pressure and venous pressure, areused when discussing blood pressure.

Technically, from the point of view of measurement, systolic pressurerefers to the pressure at which an artery becomes blocked, i.e.heartbeat stops. Physiologically, systolic pressure refers to themaximum pressure generated by a pumping cycle of the heart.

Technically, from the point of view of measurement, diastolic pressurerefers to the pressure at which heartbeat is resumed when the pressurepressing the artery is reduced. Physiologically, diastolic pressurerefers to the minimum venous pressure value between two pumping cyclesof the heart.

Venous pressure refers to the average pressure in a vein. At a certainstage of venous pressure measurement, a systolic and diastolic point canalso be detected.

Blood pressure measurement is divided into two main categories:invasive, i.e. measurement from inside the body, and non-invasive, i.e.measurement from the outside of the body. The drawback in the invasivemethod is naturally that the measurement is made from inside a person'sbody by the use of e.g. a catheter placed in an artery. The invasivemethod and the equipment solutions involved are unpleasant for a person,and the measurements involve much work and are cumbersome, since theyrequire operating theatre conditions. A special drawback is the risk ofinfection and bleeding of the artery.

Currently two methods are known for non-invasive blood pressuremeasurement, i.e. measurement from outside of the body. These includethe auscultatory measurement and the oscillometric measurement. Theauscultatory method utilizes a stethoscope and an occluding cuffprovided with a mercury manometer and a pressure pump, the cuffencircling a person's extremity, such as the arm. The auscultatorymethod is based on auscultation of sounds known as the Korotkoff soundsby the stethoscope. The Korotkoff sounds are created by blood flowing ina partially occluded artery. In the auscultatory method the pressure ofthe occluding cuff, i.e. the acting pressure, is first raised above theestimated systolic pressure, whereby blood flow in the extremity beingmeasured, such as the arm, is occluded. The pressure of the occludingcuff is then allowed to decline gradually, while the stethoscope isplaced over the artery for auscultation on the distal side with respectto the occluding cuff. Once the pressure has been lowered sufficiently,snapping Korotkoff sounds can be detected by the stethoscope, and thecurrent pressure is interpreted as the systolic pressure. Once thepressure of the occluding cuff is allowed to decline further, Korotkoffsounds are no longer heard, which means that the current pressure is thediastolic pressure at which the occluding cuff no longer occludes theartery. The drawback of the auscultatory method is its inaccuracy andthat it requires an intent and experienced user.

Publication DE-2605528 teaches an application of the auscultatory methodwhich additionally utilizes an optic pulse sensor disposed on the fingerfor following the variations in the pressure pulse. If the pressurepulse measured by the optic pulse sensor is observed to vary, thisindicates a change in blood pressure from the previous measurement, andrequires a new measurement. However, said procedure does not allowimprovement of the accuracy and reliability of a single measurement,only that said information indicates the need for a repeat measurement.

Furthermore, a manual method based on palpation is known, in whichpressure is produced by an occluding cuff in the arm, and a finger isused to palpate the pressure pulse of the radial artery, i.e. heartbeat.However, said method is inaccurate and unreliable.

Another widely used non-invasive method is the oscillometricmeasurement, in which an occluding cuff and the same principle are used,i.e. the acting pressure is first raised high, i.e. over the estimatedsystolic pressure, and then slowly declined, during which a pressuresensor comprised by the cuff is used to follow or observe the pressureoscillation signal of the cuff. Thus the essential difference ascompared with the auscultatory method is that in the oscillometricmethod an electronic monitoring unit comprised by the device is used tofollow the pressure oscillation measured by the pressure sensor insidethe cuff instead of auscultation of an artery. As cuff pressure falls,the amplitude of the pressure oscillation in the cuff, i.e. the ACsignal of the cuff pressure, increases to a certain pressure as thepressure is lowered, whereupon the oscillation decreases. When thepressure falls, oscillation, i.e. an AC-form pressure oscillationsignal, or amplitude variation, is detectable in the cuff pressure. Theamplitude of the pressure oscillation signal oscillation measured by thepressure sensor from the cuff reaches its maximum at a pressure known asmean arterial pressure. Systolic pressure can be measured relativelywell by the oscillometric method, but diastolic pressure has to becalculated indirectly since the pressure oscillation signal oscillationmeasured by the cuff pressure sensor is still present at diastolicpressure, and hence indirect determination is used, in which the valueof the diastolic pressure is the mean arterial pressure minus half ofthe difference between systolic and mean arterial pressure. A weaknessof the oscillometric method is its inaccuracy and the resultingunreliability. Oscillometric devices and methods are technically simple,but this in turn results in the inability to monitor and observe themeasurement and its reliability. The accuracy and reliability ofoscillometric measurement have been improved by different signalprocessing methods by identifying different characteristics of the ACsignal of the pressure pulse during measurement in association withdetermination of systolic and diastolic pressure. Publication U.S. Pat.No. 4,117,835, for example, discloses a method of monitoring the changein the AC signal derivative. However, in clinical measurements saidmethods have not been found to affect the accuracy.

A tonometric method, originally designed for ocular pressuremeasurement, has also been applied to blood pressure measurement. In themethods according to publication U.S. Pat. No. 5,033,471, the radialartery extending near a radius of the wrist is pressed. Since thesurface resting against the sensor is even, intravenous pressure can beread at the middle sensor element. The method thus involves a directnon-invasive measurement. In principle the measurement is ideal andpractical, but the skin causes a problem since it does not provide anideal membrane between the sensor and the blood vessel. This is whycalibration is required in tonometric methods, as described in e.g.publication U.S. Pat. No. 5,279,303.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new kind of methodand arrangement for blood pressure measurement, avoiding the problems ofknown solutions.

The object is achieved by a method according to the invention,characterized by transferring the measured value of the variablepressure acting on the measuring point at the compression point to suchan interpreting unit to which is also applied the pressure pulsegenerated by the heart and measured by a sensor at said second point fordetermining the effect of the variable acting pressure, and bydetermining diastolic pressure in the interpreting unit on the basis ofsuch an acting pressure which is measured by a measuring element andwhich is the acting pressure when the interpreting unit detects asufficiently long-standing change in a pressure pulse signal measured bysaid sensor.

The object is achieved by a method according to the invention,characterized by transferring the measured value of the variablepressure acting on the measuring point at the compression point to suchan interpreting unit to which is also applied the pressure pulsegenerated by the heart and measured by a sensor at said second point fordetermining the effect of the variable acting pressure, and bydetermining systolic pressure in the interpreting unit on the basis ofsuch an acting pressure which is the acting pressure when theinterpreting unit detects a sufficiently long-standing change in apressure pulse signal measured by said sensor.

The measurement arrangement of the invention is characterized by usingas the sensor for measuring the effect of the variable acting pressureat the second point said sensor which measures the pressure pulsegenerated by heartbeat and which is coupled to such an interpreting unitto which is also coupled a measured signal indicating the measured valueof the acting pressure, and that the interpreting unit is arranged todetermine diastolic pressure on the basis of such an acting pressurewhich is the pressure acting when the interpreting unit detects a changecharacteristic of diastolic pressure in a pressure pulse signal measuredby the sensor which measures the artery.

The measurement arrangement of the invention is characterized by usingas the sensor for measuring the effect of the variable acting pressureat the second point said sensor which measures the pressure pulsegenerated by heartbeat and which is coupled to such an interpreting unitto which is also coupled a measured signal indicating the measured valueof the acting pressure, and that the interpreting unit is arranged todetermine systolic pressure on the basis of such an acting pressurewhich is the pressure acting when the interpreting unit detects a changecharacteristic of systolic pressure in a pressure pulse signal measuredby the sensor which measures the artery.

The method and measurement arrangement of the invention are based on theidea of using a sensor, which measures the pressure pulse and transfersits measurement data to the interpreting unit, to indicate from themeasured acting pressure signal the points conforming with diastolicand/or systolic pressure.

The solution of the invention provides a plurality of advantages. Theinvention provides an extremely good measurement accuracy, allowingsystolic and/or diastolic pressure to be determined extremelyaccurately, since their detection is based on a separate measurement ofthe pressure pulse, which is used to indicate the values of saidsystolic and/or diastolic pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail withreference to the attached drawings, in which

FIG. 1 shows a first embodiment of the measurement arrangement,

FIG. 2 shows a second embodiment of the measurement arrangement,

FIG. 3 shows a third embodiment of the measurement arrangement,

FIG. 4 shows blood pressure measurement during a rising acting pressure,

FIG. 5 shows blood pressure measurement during a falling actingpressure,

FIG. 6 shows an embodiment for transferring measurement data on theacting pressure and on the pressure pulse to the interpreting unit,

FIG. 7 shows the inner structure of the interpreting element comprisedby the interpreting unit.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method and an arrangement for blood pressuremeasurement. The measurement arrangement will be described first. Themeasurement arrangement comprises a cuff-like or other type of pressuregenerator 1, for applying pressure to a measuring point 3, such as aperson's extremity 3 or the like, at a compression point A. Thecuff-type pressure generator 1 obtains its pressure from a pressuresource 1 a, comprised by the arrangement, via a pressure line 1 b. Thepressure source 1 a can be e.g. a pump.

The pressure serves to occlude the artery in the extremity 3 uponpressing and to open the artery when the pressure is released. Thearrangement further comprises an element 5 for measuring the magnitudeof the pressure generated by the pressure generator 1 for applying thepressure to the compression point A. The measuring element 5 can be e.g.a Si pressure sensor or other DC pressure sensor. The arrangementfurther comprises a sensor 7 for simultaneously measuring the effect ofthe variable acting pressure on an artery at a second point B. Thesensor 7 can be e.g. a PVDF sensor (PolyVinylDiFluoride) or an EMFsensor (Electro Mechanical Film). Said second point B is a point whichis farther away from the heart, i.e. closer to the end point ofperipheral circulation than the compression point A, to which thepressure is applied. The measuring point B is thus at the distal, i.e.peripheral, side of the circulation. The measurement arrangement furthercomprises an interpreting means 9 for determining systolic and/ordiastolic pressure. The interpreting unit 9 does not necessarily have tobe a separate unit, but can also be integrated with the other means.

Said sensor 7 measures at the second point B the pressure pulse causedby heartbeat and is preferably separate from the pressure generator. Thesensor 7 is coupled to said interpreting unit 9, to which a measuringsignal, which is obtained from the measuring element 5 and depicts themeasurement value of the acting pressure, is also coupled. In FIGS. 1and 3, arrow 105 shows the transfer of the acting pressure from themeasuring element 5 to the interpreting unit 9 in a simplified manner.The pressure pulse is preferably measured by a sensor 7 which, at leastfrom the point of view of the technical operation of the measurement, isseparate from the pressure generator, i.e. the sensor 7 measures thepressure pulse, i.e. the effect of the acting pressure, independently,not from the same signal source as the measuring element 5 measuring theacting pressure.

In some embodiments the sensor 7 can be in connection with the pressuregenerator or parts in connection therewith by e.g. a rod or conductor orotherwise, but in this case the pressure generator must be of a typewhich does not interfere with the operation of the sensor.

According to FIGS. 1 and 3, in the measurement arrangement saidinterpreting unit 9 is preferably a wristband-type unit 9, which in FIG.1 comprises a pressure pulse sensor 7 for measuring the artery. Thismakes the measurement arrangement integrated and compact. In thispreferred embodiment the method is such that the measured signalcomprising the measured value of the acting pressure is transferred tosaid wristband type of interpreting unit, said interpreting unit 9 alsobeing arranged to measure the pressure pulse by means of said pressurepulse measuring sensor 7 comprised by (FIG. 1) the interpreting unit 9or being otherwise in connection (FIG. 3) therewith.

Referring to FIG. 2, an alternative solution can involve a separateinterpreting unit, implemented by e.g. a microcomputer/measuring deviceor the like, the sensor 7 measuring the arterial pressure pulse signalbeing in a wired connection 21 or in a wireless connection 22 with saidinterpreting unit 9. The wired connection 21 could be e.g. a cable 21between the sensor 7 and the interpreting unit 9, i.e. acomputer/measuring device provided with e.g. a measuring card. In FIG.2, a dashed line 22 denotes a wireless connection between the arterialpressure pulse sensor 7 and the interpreting unit 9. The wirelessconnection 22 is preferably implemented by a magnetic inductive coupling22 a, 22 b, comprising a transmitter element 22 a controlled by thesensor 7 and comprising a coil, and a receiver element 22 b disposed inthe interpreting unit 9 and comprising a second coil.

A combination of the previous versions, i.e. a third embodiment inaccordance with FIG. 3, is also feasible, i.e. the interpreting unit 9can be a wristband-type unit, but in FIG. 3 the pressure pulse sensor 7measuring the artery is not integrated with the interpreting unit 9, butis in a wired connection 31 or a wireless connection 32 with theinterpreting unit 9. The connections 31, 32 can be implemented in thesame way as was presented for the version of FIG. 2, i.e. by a cable 31or as a magnetic inductive coupling 32. Reference numerals 32 a, 32 bdenote the transmitter element 32 a and receiver element 32 b of thewireless telemetric magnetic inductive coupling.

In a preferred embodiment of the invention the pressure pulse sensor 7is a multichannel sensor, most preferably a line sensor, i.e. an arraysensor. In this case the pressure pulse is measured as a multichannelmeasurement. The different channels 7 a to 7 d of the multichannel linesensor 7 are shown in FIG. 1 in a simplified form. This provides a morereliable measurement result than with a mere single-channel sensor. Thedifferent channels 7 a to 7 d of the multichannel sensor 7 are shown inFIG. 1 in a simplified manner.

In a preferred embodiment, the pressure pulse is measured in the radialartery area, where the arterial pressure pulse is easily detectable, andwhich is an easy point from the point of view of the subject of themeasurement.

Referring to FIGS. 1 to 6, in the measurement arrangement saidinterpreting unit 9 is arranged to determine diastolic pressure PDIASand systolic pressure PSYS on the basis of an acting pressure which isthe acting pressure when a change characteristic of diastolic pressurePDIAS and a change characteristic of systolic pressure PSYS are detectedby the interpreting unit 9, more exactly by the interpreting element 9 acomprised by it, in the pressure pulse signal measured by the sensor 7measuring the artery (the arterial pressure pulse).

A measurement arrangement of the type described above allows theimplementation of a method for blood pressure measurement, the methodcomprising applying a variable compressive acting pressure to ameasuring point, such as a person's extremity 3 or the like measuringpoint 3 at a compression point A, and at the same time the effect of thevariable acting pressure on the artery is measured at a second point B.The method is characterized by transferring the measured value of thevariable pressure acting on the measuring point at the compression pointA from the measuring element 5 to an interpreting unit 9 to which isalso applied the magnitude, preferably amplitude, of the pressure pulsegenerated by the heart and measured by the sensor 7 at said second pointB. As was stated above, the sensor 7 is preferably separate from thepressure generator 1, i.e. the cuff 1, whereby in the preferredembodiment the pressure pulse is measured with the sensor 7 at a pointwhich is at least as far away from the pressure generator 1 as the pointto which the reach area of the pressure oscillation of the pressuregenerator extends. In this case the pressure variation in the cuff 1does not interfere with the measurement of the pressure pulse. Themethod is characterized by determining diastolic pressure PDIAS in theinterpreting unit 9 on the basis of an acting pressure which is theacting pressure when the interpreting unit 9 detects a sufficientlylong-lasting change in the magnitude, preferably amplitude, of thepressure pulse signal measured by said sensor 7. As regards systolicpressure PSYS, the method is characterized in that systolic pressure ismeasured in the interpreting unit 9 on the basis of a second actingpressure which is the acting pressure when the interpreting unit 9detects a sufficiently long-lasting change of a second type in themagnitude, for example amplitude, of the pressure pulse signal measuredby said sensor 7.

In the embodiments disclosed in the present application the pressurepulse is most preferably measured as an amplitude measurement, andnaturally monitoring the magnitude of the pressure pulse is also basedon monitoring amplitude values. However, instead of amplitude, thesensor 7 can measure pressure pulse frequency or phase, which also serveto indicate the magnitude of the pressure pulse, and hence, amplitude.The measurement may also involve amplitude measurement, amplitude databeing converted into frequency or phase data. Thus the present inventionis not only restricted to direct amplitude measurement and comparison bymeans of amplitude.

In the method, the measurement of the variable acting pressure with themeasuring element 5 and the measurement of the pressure pulse, e.g. itsamplitude, with the sensor 7 are used to form the magnitude of thepressure pulse, such as amplitude data, as a function of the actingpressure. Systolic pressure PSYS and/or diastolic pressure PDIAS isdetermined in the interpreting unit 9 on the basis of said function. Thesensor 7, which is preferably physically completely separate from thepressure generator 1, i.e. the cuff 1, consequently operates as anindicator of the interpreting unit 9, indicating to the interpretingunit 9 whether the magnitude of the acting pressure of the cuff 1indicates the magnitude of diastolic pressure PDIAS or the magnitude ofsystolic pressure PSYS.

In a preferred embodiment, unlike in methods and arrangements employingthe conventional determination of the acting pressure during fallingacting pressure, the method employs rising acting pressure in accordancewith FIG. 4. In this case the blood pressure measurement is carried outwhen the acting pressure is raised. Measurement during rising pressureis more convenient to the subject, since the acting pressure does nothave to be raised too high. This situation involves determination ofdiastolic pressure PDIAS in a measurement during rising acting pressureon the basis of an acting pressure equal to the pressure acting when theinterpreting unit 9 detects during measurement of the pressure pulse,e.g. its amplitude, by the sensor 7, that the magnitude of the pressurepulse, e.g. its amplitude, starts to fall. Similarly, systolic pressurePSYS is determined on the basis of an acting pressure equal to thepressure acting when the interpreting unit 9, 9 a detects duringmeasurement of the pressure pulse, e.g. its amplitude, by the sensor 7,that the magnitude of the pressure pulse, e.g. its amplitude, stopsfalling.

More specifically and still referring to FIG. 4, the method ispreferably such that in a measurement made during rising actingpressure, diastolic pressure PDIAS is determined on the basis of anacting pressure equal to the pressure acting when it is detected duringmeasurement of the pressure pulse, e.g. its amplitude, that anessentially constant value of the pressure pulse, e.g. its amplitude,starts to fall substantially linearly. In FIG. 4 said constant amplituderange is denoted by SA, and the linear range is denoted by L. Similarly,systolic pressure PSYS is determined on the basis of an acting pressureequal to the pressure acting when it is detected during measurement ofthe pressure pulse, e.g. its amplitude, that the amplitude of thesubstantially directly linearly falling pressure pulse stops falling andreaches its minimum value AMIN, which substantially corresponds to zero.It is easier to detect such points by the sensor 7 and the interpretingunit 9, and a more accurate measurement is also achieved.

An alternative is a second preferred embodiment in accordance with FIG.5, in which said variable acting pressure is a falling acting pressure,and blood pressure is measured as the acting pressure is lowered. Themethod is most preferably such that systolic pressure PSYS is determinedin a measurement during falling acting pressure on the basis of anacting pressure equal to the pressure which is acting when theinterpreting unit 9 detects in a signal measured by the sensor 7 in apressure pulse measurement that the amplitude of the pressure pulsestarts to increase. Similarly, diastolic pressure PDIAS is determined onthe basis of an acting pressure equal to the pressure acting when theinterpreting unit 9 detects in a signal measured by the sensor 7 in apressure pulse measurement that the amplitude of the pressure pulsestops increasing.

More specifically and still referring to FIG. 5, the method ispreferably such that in a measurement made during falling actingpressure, systolic pressure PSYS is determined on the basis of an actingpressure equal to the pressure acting when the interpreting unit 9detects during measurement of the pressure pulse by the sensor 7 thatthe amplitude of the pressure pulse starts to increase from its minimumamplitude value AMIN which substantially corresponds to zero. Similarly,diastolic pressure PDIAS is determined on the basis of an actingpressure equal to the pressure acting when the interpreting unit 9detects during a pressure pulse measurement made by the sensor 7 thatthe amplitude of the pressure pulse stops increasing and reaches itsconstant value, such as the amplitude value SA having constantamplitude.

It is easier to detect such precisely shaped points and ranges by theinterpreting unit 9, and a more accurate measurement is also achieved.

FIG. 6 shows an embodiment for transferring measurement data measured bythe acting pressure measuring element 5 in connection with the pressuregenerator to the interpreting unit 9. FIG. 6 also shows an embodimentfor processing the signal measured by the pressure pulse sensor 7 andfor transferring it to the interpreting unit 9.

Referring to FIG. 6, a preferred embodiment of the invention involves ameasurement arrangement comprising a wireless telemetric magneticinductive coupling 101, 102 for transferring the measured actingpressure measuring signal from the measuring element 5 to theinterpreting unit 9. Said coupling comprises a transmitter element 101,which obtains input data from the acting pressure measuring element 5,and a receiver element 102 in the interpreting unit 9. The transmitterelement 101 comprises a coil 101 a, to which the signal measured by themeasuring element 5 is applied. The receiver element 102 comprises asecond coil 102 a. In the method the acting pressure measurement valueis transferred to the interpreting unit 9 as a wireless telemetrictransfer by means of the magnetic inductive coupling 101, 102 betweenthe coils 101 a, 102 a. The connection 105 for transferring the signalmeasured by the acting pressure measuring element 5 to the interpretingunit 9, shown in FIGS. 1 and 3 in a simplified manner by arrow 105, canbe a wired connection or wireless, as the transfer implemented by theinductive coupling by the components 101, 102 in FIGS. 2 and 6.

In accordance with FIG. 6, in a preferred embodiment the measurementarrangement comprises an amplifier 110 and a filter 111 for amplifyingand filtering the pressure pulse signal measured by the sensor 7, and anA/D converter 112 for performing A/D conversion after filtering. Theamplifier 110 can be e.g. a voltage or charging amplifier. The filter111, in turn, is preferably a band-pass filter whose passband is e.g.within the range 1 to 10 Hz.

The method is preferably such that the pressure pulse signal measured bythe sensor 7 is amplified by the amplifier 110 and filtered by thefilter 111, and then A/D converted by the converter 112. Theamplification and filtering serve to eliminate interference anddistortion, resulting in a sufficiently strong signal. The A/Dconversion, in turn, converts the measured signal into a form which theinterpreting unit 9 is able to interpret and process. FIGS. 2, 5 and 7show the interpreting element 9 a, e.g. a microprocessor, comprised bythe interpreting unit 9. The versions shown by the other figures alsocomprise a similar component.

In fact, FIG. 7 shows the inner structure of the interpreting element 9a comprised by the interpreting unit 9. In FIG. 7, the interpretingelement 9 a comprises a part 901 for identifying the active pressuremeasurement signal, a part 902 for identifying the pressure pulsesignal, a signal check part 903 connected to parts 901 and 902, astraight line fitting part 904 connected to part 903 and a SYS/DIASdetermining part 905 connected to part 904. The SYS/DIAS determiningpart 905 determines the values of systolic and/or diastolic pressureaccording to what the straight line fitting algorithm (least squaresprinciple) in the straight line fitting part 903 indicates on the basisof the received pressure measuring signal and pressure pulse signal. Thestraight line fitting algorithm serves to convert a discrete measurementinto a form with continuous values.

In a preferred embodiment the interpreting unit 9 a comprises, or atleast has a connection to, a memory 906 and a display 907. The memory906 and the display 907 can be external parts with respect to theinterpreting element 9 a, belonging, however, to the interpreting unit9.

In the most practical solution of the measurement arrangement of apreferred embodiment both diastolic and systolic pressure aredetermined. In this case both diastolic and systolic pressure aredetermined by common means 5, 7, 9, 901 to 907. This makes the methodand the measurement arrangement more usable.

In a preferred embodiment of the invention the measurement arrangementcomprises an amplifier 210 and a filter 211 for filtering the actingpressure measuring signal obtained from the measuring element 5 tofilter off an oscillating AC portion caused by the pulse. The measuringelement 5 carries out a pressure/voltage conversion, for example, and inthis case the amplifier 210 is a voltage amplifier. The filter 211, inturn, is a low-pass filter with an upper limit frequency of e.g. 1 to 5Hz.

In a preferred embodiment, the arrangement further comprises an A/Dconverter 212 for AND conversion of the filtered acting pressure signal.If an inductive coupling 101, 102 is used for transferring the signalmeasured by the acting pressure measuring element 5 to the interpretingunit 9, then the arrangement further comprises a modulator 213 oranother signal modulator unit 213 for modulating the AND convertedsignal e.g. to a frequency modulated signal or to another signal whichcan be applied to the transmitter unit 101 comprised by the inductivecoupling. The signal modulator unit 213 can be e.g. a pulse widthmodulator or a frequency modulator. Together the blocks 212 and 213 forma signal modulator 215 which serves to modulate the signal into atransferable form for the transmitter element 101. It should be observedthat the connection 101-102 could alternatively be optic.

Said units 210 to 213 and 101 are most preferably part of the sameentity as are the measuring unit 5 and the pressure generator 1. Themethod thus preferably comprises a step of filtering the measured actingpressure signal by the filter 211 to filter off an oscillating ACportion caused by heartbeat. In said preferred embodiment, thedetermination of systolic pressure PSYS and diastolic pressure PDIASemploy the filtered acting pressure of the measured signal, obtained byfiltration, and the information contained therein is transferred to theinterpreting unit 9. The measured acting pressure signal is preferablyamplified by the amplifier 210 before the measured acting pressuresignal is filtered, and A/D conversion by the A/D converter 212 iscarried out after filtration. In other words, the solution of thepreferred embodiment employs in determining systolic pressure PSYS anddiastolic pressure PDIAS an acting pressure signal which has beensubjected to A/D conversion and from which the interpreting unit 9calculates the blood pressure values from the measured signaloriginating from the measuring element 5 by using as indicator thesignal of the sensor 7 measuring the artery. Thus the portion obtainedfrom the filtration of the acting pressure measured by the measuringelement 5 in connection to the pressure generator 1, i.e. the cuff 1, isthe acting pressure from which the arterial pressure pulse measuringsensor 7 “indicates” the blood pressure values. Filtering off the ACportion, i.e. the use of a filtered acting pressure, results in anacting pressure measurement result having less interference, since theeffect of heartbeat, which causes AC oscillation in the acting pressure,on the cuff can be eliminated by filtration.

The magnetic inductive coupling described above in different contexts,is based on applying a current with varying magnitude to the coil of thetransmitter element, the coil generating a magnetic field with varyingmagnitude, the field being received by a second coil, i.e. by the coilof the receiver element. A magnetic inductive coupling is useful insmall portable devices owing to its low power consumption. An inductivecoupling is particularly useful in wristband-type versions according toFIGS. 1 and 3.

The preferred embodiments of the invention described above and the otherfeatures of the method and measurement arrangement presented in greaterdetail highlight the advantages of the basic invention.

Although the invention is described herein with reference to theexamples in accordance with the accompanying drawings, it will beappreciated that the invention is not to be so limited, but can bemodified in a variety of ways within the scope of the inventive ideadisclosed in the appended claims.

What is claimed is:
 1. A method for blood pressure measurement,comprising applying a variable compressive acting pressure to ameasuring point at a compression point by a pressure generator, and atthe same time using a sensor to measure an arterial pressure pulse underthe effect of the variable acting pressure on the artery at a secondpoint, the second point being located farther away from the heart thanthe compression point to which the acting pressure is applied,characterized by providing a signal representing the measured value ofthe variable pressure acting on the measuring point at the compressionpoint to an interpreting unit, sending a pressure pulse signalrepresenting the measured arterial pressure pulse from the sensor to theinterpreting unit, and determining diastolic pressure in theinterpreting unit on the basis of the variable acting pressure when theinterpreting unit detects a change in trend in a characteristicindicative of the magnitude of the pressure pulse in the pressure pulsesignal from said sensor.
 2. A method as claimed in claim 1,characterized in that pressure pulse measurement data is generated as afunction of the acting pressure on the basis of the measurement of thevariable acting pressure employed in the method and the measurement ofthe pressure pulse, systolic and/or diastolic pressure being determinedin the interpreting unit on the basis of said function.
 3. A method asclaimed in claim 1, characterized in that said variable acting pressureis a falling acting pressure, and that blood pressure is measured whenthe acting pressure is lowered.
 4. A method as claimed in claim 3,characterized in that in the measurement performed during falling actingpressure, systolic pressure is determined on the basis of an actingpressure equal to the pressure acting when it is detected in pressurepulse measurement that the magnitude of the pressure pulse starts toincrease.
 5. A method as claimed in claim 1, characterized in that thepressure pulse is measured in the area of the radial artery.
 6. A methodas claimed in claim 1, characterized in that the pressure pulse ismeasured as a multichannel measurement.
 7. A method as claimed in claim6, characterized in that the pressure pulse is measured by a linesensor.
 8. A method as claimed in claim 1, characterized by transferringthe measured signal containing the measured value of the acting pressureto said wristband type of interpreting unit, which is also arranged tomeasure the pressure pulse by means of said pressure pulse measuringsensor comprised by it or otherwise being in connection thereto.
 9. Amethod as claimed in claim 1, characterized by transferring the measuredvalue of the acting pressure to the interpreting unit as a wirelesstelemetric transfer by means of a magnetic inductive coupling.
 10. Amethod as claimed in claim 1, characterized in that the pressure pulsesignal measured by the sensor is amplified and filtered, and thensubjected to A/D conversion.
 11. A method as claimed in claim 1,characterized in that the measured acting pressure signal is filtered tofilter off the oscillating AC portion caused by heartbeat to generate ameasured filtered acting pressure signal.
 12. A method as claimed inclaim 11, characterized in that the filtered measured acting pressuresignal is used in the determination of systolic and/or diastolicpressure.
 13. A method as claimed in claim 11, characterized in thatbefore the measured acting pressure signal is filtered, it is amplified,and after filtration subjected to conversion to modify it to atransferable form, and that said signal conversion includes A/Dconversion followed by modulation.
 14. A method as claimed in claim 1,characterized by measuring both diastolic and systolic pressure, and bysaid change in trend in a characteristic indicative of the magnitude ofthe pressure pulse, observed by the pressure pulse meaning sensor, beingdifferent for diastolic and for systolic pressure.
 15. A method asclaimed in claim 1, characterized in that the pressure pulse is measuredwith the sensor from a point which is at least as far away from thepressure generator as the point to which the reach area of the pressureoscillation of the pressure generator extends.
 16. A method as claimedin claim 15, characterized in that an inflatable cuff is used as thepressure generator.
 17. A method as claimed in claim 1, characterized inthat the pressure pulse is measured with a sensor which is separate fromthe pressure generator at least from the point of view of the technicaloperation of the measurement.
 18. A method as claimed in claim 1,characterized in that the pressure pulse is measured with a sensor whichis physically detached from the pressure generator.
 19. A method asclaimed in claim 1, characterized in that the sensor measures theamplitude, frequency or phase of the pressure pulse.
 20. A method forblood pressure measurement, comprising applying a variable compressiveacting pressure to a measuring point, at a compression point by apressure generator, and at the same time using a sensor to measure anarterial pressure pulse under the effect of the variable acting pressureon the artery at a second point, the second point located farther awayfrom the heart than the compression point to which the acting pressureis applied, characterized by providing a signal representing themeasured value of the variable pressure acting on the measuring point atthe compression point to an interpreting unit, sending a pressure pulsesignal representing the measured arterial pressure pulse from the sensorto the interpreting unit, and determining systolic pressure in theinterpreting unit on the basis of the variable pressure when theinterpreting unit detects a change in trend in a characteristicindicative of the magnitude of the pressure pulse in the pressure pulsesignal from said sensor.
 21. A method for blood pressure measurement,comprising: applying a variable compressive acting pressure to ameasuring point at a compression point by a pressure generator, whereinsaid variable acting pressure is a rising acting pressure, and at thesame time using a sensor to measure an arterial pressure pulse under theeffect of the variable acting pressure on the artery at a second point,the second point being located farther away from the heart than thecompression point to which the acting pressure is applied, providing asignal representing the measured value of the variable pressure actingon the measuring point at the compression point to an interpreting unit,sending a pressure pulse signal representing the measured arterialpressure pulse from the sensor to the interpreting unit, and determiningdiastolic pressure in the interpreting unit on the basis of an actingpressure equal to the pressure acting when it is detected in pressurepulse measurement that the magnitude of the pressure pulse signal fromsaid sensor starts to decrease.
 22. A method as claimed in claim 21,characterized in that in the measurement performed during rising actingpressure, diastolic pressure is determined on the basis of an actingpressure equal to the pressure acting when it is detected in pressurepulse measurement that the substantially constant value of the pressurepulse starts to decrease substantially linearly.
 23. A method for bloodpressure measurement, comprising: applying a variable compressive actingpressure to a measuring point at a compression point by a pressuregenerator, wherein said variable acting pressure is a rising actingpressure, and at the same time using a sensor to measure an arterialpressure pulse under the effect of the variable acting pressure on theartery at a second point, the second point located farther away from theheart than the compression point to which the acting pressure isapplied, providing a signal representing the measured value of thevariable pressure acting on the measuring point at the compression pointto an interpreting unit, sending a pressure pulse signal representingthe measured arterial pressure pulse from the sensor to the interpretingunit, and determining systolic pressure in the interpreting unit on thebasis of an acting pressure equal to the pressure acting when it isdetected in pressure pulse measurement that the magnitude of thepressure pulse signal from said sensor stops decreasing.
 24. A method asclaimed in claim 23, characterized in that systolic pressure isdetermined on the basis of an acting pressure equal to the pressureacting when it is detected in pressure pulse measurement that themagnitude of the pressure pulse, which decreases substantially directlylinearly, stops decreasing and reaches its minimum value, whichsubstantially corresponds to zero.
 25. A method for blood pressuremeasurement, comprising: applying a variable compressive acting pressureto a measuring point at a compression point by a pressure generator,wherein said variable acting pressure is a falling acting pressure, andat the same time using a sensor to measure an arterial pressure pulseunder the effect of the variable acting pressure on the artery at asecond point, the second point being located farther away from the heartthan the compression point to which the acting pressure is applied,providing a signal representing the measured value of the variablepressure acting on the measuring point at the compression point to aninterpreting unit, sending a pressure pulse signal representing themeasured arterial pressure pulse from the sensor to the interpretingunit, and determining diastolic pressure in the interpreting unit on thebasis of an acting pressure equal to the pressure acting when it isdetected in pressure pulse measurement that the magnitude of thepressure pulse signal from said sensor stops increasing.
 26. A method asclaimed in claim 25, characterized in that diastolic pressure isdetermined on the basis of an acting pressure equal to the pressureacting when it is detected in pressure pulse measurement that themagnitude of the pressure pulse stops increasing and reaches a constantvalue.
 27. A method for blood pressure measurement, comprising: applyinga variable compressive acting pressure to a measuring point at acompression point by a pressure generator, wherein said variable actingpressure is a falling acting pressure, and at the same time using asensor to measure an arterial pressure pulse under the effect of thevariable acting pressure on the artery at a second point, the secondpoint located farther away from the heart than the compression point towhich the acting pressure is applied, providing a signal representingthe measured value of the variable pressure acting on the measuringpoint at the compression point to an interpreting unit, sending apressure pulse signal representing the measured arterial pressure pulsefrom the sensor to the interpreting unit, and determining systolicpressure in the interpreting unit on the basis of an acting pressureequal to the pressure acting when it is detected in pressure pulsemeasurement that the magnitude of the pressure pulse signal from saidsensor starts to increase from its minimum value which substantiallycorresponds to zero.
 28. An arrangement for blood pressure measurement,comprising a pressure generator for applying a compressive actingpressure to a measuring point, an acting pressure measuring element, aninterpreting unit arranged to determine diastolic pressure, a sensor forsimultaneous measurement of the effect of the variable acting pressureon an artery at a second point and for generating a pressure pulsesignal representing a measured arterial pressure pulse, said secondpoint being farther away from the heart, i.e, closer to the end point ofperipheral circulation, than the compression point to which the actingpressure is applied, said sensor which measures the pressure pulsegenerated by heartbeat being coupled to said interpreting unit to whichis also coupled the acting pressure measuring element, and that theinterpreting unit is arranged to determine diastolic pressure on thebasis of an acting pressure which is the pressure acting when theinterpreting unit detects a change characteristic of diastolic pressurein a pressure pulse signal measured by the sensor which measures theartery.
 29. An arrangement as claimed in claim 28, characterized in thatsaid interpreting unit is a wristband or other type of unit comprisingsaid pressure pulse sensor measuring the artery.
 30. An arrangement asclaimed in claim 28, characterized in that said interpreting unit is awristband or other type of unit which is in a wireless connection or awired connection to said pressure pulse sensor measuring the artery. 31.An arrangement as claimed in claim 28, characterized in that thepressure pulse sensor is a multichannel sensor.
 32. An arrangement asclaimed in claim 28, characterized in that for transferring the measuredacting pressure value to the interpreting unit, the arrangementcomprises a wireless transmitter which receives input data from theacting pressure measuring element and a wireless receiver element in theinterpreting unit.
 33. An arrangement as claimed in claim 32,characterized by comprising a signal modulator for modulating thefiltered acting pressure signal into a form suitable for the transmitterelement before the signal is coupled to the transmitter element.
 34. Anarrangement as claimed in claim 33, characterized in that the signalmodulator comprises a signal modulator unit (213).
 35. An arrangement asclaimed in claim 34, characterized in that the signal modulator unit amodulator, such as a pulse width modulator, frequency modulator or othermodulator.
 36. An arrangement as claimed in claim 34, characterized inthat the signal modulator comprises and A/D converter which precedes thesignal modulator unit and is used for A/D conversion of the measuredfiltered acting pressure signal.
 37. An arrangement as claimed in claim34, characterized in that diastolic and systolic pressure are determinedby common means.
 38. An arrangement claimed in claim 28, characterizedin that for transferring the measured acting pressure value to theinterpreting unit, the arrangement comprises a wireless telemetricmagnetic inductive coupling comprising a wireless transmitter whichreceives input data from the acting pressure measuring element and awireless receiver element in the interpreting unit.
 39. An arrangementas claimed in claim 28, characterized by comprising an amplifier and afilter for amplifying and filtering the pressure pulse signal measuredby the sensor, and an A/D converter for performing A/D conversion afterthe filtering.
 40. An arrangement as claimed in claim 28, characterizedby comprising a filter for filtering the measured acting pressure signalto filter off the oscillating AC portion for generating a measuredfiltered acting pressure signal.
 41. An arrangement as claimed in claim40, characterized in that before the filter for filtering off the ACportion, the arrangement comprises an amplifier for amplifying themeasured acting pressure signal.
 42. An arrangement as claimed in claim40, characterized in that the filter which filters off the AC portion isa low-pass filter.
 43. An arrangement as claimed in claim 42,characterized in that the upper limit frequency of the low-pass filteris between 1 and 5 Hz.
 44. An arrangement as claimed in claim 28,characterized in that the measurement arrangement is arranged todetermine both diastolic and systolic pressure.
 45. An arrangement asclaimed in claim 28, characterized in that an inflatable cuff is used asthe pressure generator.
 46. An arrangement as claimed in claim 28,characterized in that the pressure pulse is measured by the sensor at apoint which is at least as far ways from the pressure generator as thepoint to which the reach area of the pressure oscillation of thepressure generator extends.
 47. An arrangement as claimed in claim 28,characterized in that the pressure pulse is measured by the sensor whichis separate from the pressure generator at least from the point of viewof the technical operation of the measurement.
 48. An arrangement asclaimed in claim 28, characterized in that the pressure pulse ismeasured by a measuring sensor which is physically separate from thepressure generator.
 49. An arrangement for blood pressure measurement,comprising a pressure generator for applying a compressive actingpressure to a measuring point, such as a person's extremity, thearrangement comprising an acting pressure measuring element, aninterpreting unit arranged to determine systolic pressure, a sensor forsimultaneous measurement of the effect of the variable acting pressureon an artery at a second point and for generating a pressure pulsesignal representing a measured arterial pressure pulse, said secondpoint being farther away from the heart than the compression point towhich the acting pressure is applied, said sensor which measures thepressure pulse generated by heartbeat being coupled to said interpretingunit to which is also coupled the acting pressure measuring element, andthat the interpreting unit is arranged to determine systolic pressure onthe basis of an acting pressure which is the pressure acting when theinterpreting unit detects a change characteristic of systolic pressurein a pressure pulse signal measured by the sensor which measures theartery.
 50. An arrangement as claimed in claim 49, characterized in thatthe pressure pulse sensor is a line sensor.
 51. An apparatus fordetermining systolic blood pressure comprising: a pressure cuff forapplying a variable pressure to a person's extremity; a pressuregenerator connected to said pressure cuff, said pressure generatorproviding said variable pressure to said pressure cuff; a measuringelement for measuring the variable pressure provided by said pressuregenerator; a sensor, said sensor being capable of detecting a pressurepulse in an artery in said extremity, said sensor capable of creating apressure pulse signal; and an interpreting unit connected to saidmeasuring element and said sensor for determining systolic pressure,said interpreting unit being capable of determining said systolicpressure on the basis of the variable pressure measured by the measuringelement and a change in trend in a characteristic indicative of themagnitude of the pressure pulse in the pressure pulse signal receivedfrom said sensor.
 52. An apparatus for determining diastolic bloodpressure comprising: a pressure cuff sized to fit around a person'sextremity, said pressure cuff being capable of being inflated tovariable pressures; a pressure generator, said pressure generator beingconnected to said pressure cuff to create said variable pressure, ameasuring element for measuring the variable pressure provided by saidpressure generator; a sensor, said sensor being capable of detecting apressure pulse in an artery in said extremity, said sensor capable ofcreating a pressure pulse signal; and an interpreting unit, saidinterpreting unit being connected to said sensor and to said measuringelement, said interpreting unit being capable of determining diastolicpressure on the basis of the variable pressure measured by the measuringelement and a change in trend in a characteristic indicative of themagnitude of the pressure pulse in the pressure pulse signal receivedfrom said sensor.